Mass spectrometer having a concentric cylindrical electrode structure



March 1966 HANS GEORG NCSLLER 3,239,652

MASS SPECTROMETER HAVING A CONCENTRIG CYLINDRICAL ELECTRODE STRUCTUREFiled Sept. 30, 1965 2 Sheets-Sheet 1 GT0 mCl/l/M r x e z e m WW? Z a GMarch I966 HANS GEORG NOLLER 3,239,662

MASS SPECTROMETER HAVING A CONCENTRIC CYLINDRICAL ELECTRODE STRUCTUREFiled Sept. 30, 1965 3 Sheets-Sheet 2 r0 l/ACUUM srsmw TTO/QA/EX UnitedStates Patent 3,239,662 MASS SPECTROMETER HAVING A CONCENTRICCYLINDRICAL ELECTRODE STRUCTURE Hans Georg Niiller, Munchkuhrweg 31,Walherberg, Bezirk Bonn, Germany Filed Sept. 30, 1963, Ser. No. 313,723Claims priority, application Germany, Oct. 9, 1962,

Claims. (51. 250-413 This invention relates to a mass spectrometer andis particularly suited for use as a vacuum leak detector.

Mass spectrometers are known in which ions are created by electroncollision and in which these ions are subjected to electric and magneticfields. By these means there occurs a spatial separation of the ionsaccording to their masses so that ions of a certain mass are collectedon a collector electrode and thereby measured. For example, magneticsector field mass spectrometers are known in which the ions are directedthrough focusing electric and magnetic fields in succession beforecollection by a collecting electrode. Also known are cycloidal massspectrometers in which the ions are simultaneously subjected to ahomogenous electric and to a homogenous magnetic field beforecollection. These known devices have in general suffered from one ormore of the following disadvantages: low sensitivity, excessive size,high cost, etc.

The objective of this invention is to provide a mass spectrometer whichis simpler, smaller, less expensive, and exhibits a high sensitivity sothat components with very small partial pressure can be determined in agas mixture.

One feature of this invention is the provision of a crossed field massspectrometer wherein a cylindrical condenser provides a cylindricallysymmetrical electrical field whose axis of symmetry is parallel to anapplied magnetic force.

Another feature of this invention is the provision of a massspectrometer of the above-featured type which includes an electronsource for producing ionization within the outer electrode of thecylindrical condenser.

Another feature of this invention is the provision of a massspectrometer of the first featured type which includes an ion source fordirecting a beam of ions into the electric field produced by thecylindrical condenser.

Another feature of this invention is the provision of a massspectrometer of the above-featured type wherein the outer electrode ofthe cylindrical condenser is provided with an aperture for the injectionof an ion beam and an aperture for the withdrawal of an ion signal.

Another feature of this invention is the provision of a massspectrometer of the above-featured types including an aperturedcylindrical electrode bafile which is concentrically positioned betweenthe electrodes of the cylindrical condenser and is selectively aperturedto allow passage of ions having a desired mass.

Another feature of this invention is the provision of a cylindricalcondenser mass spectrometer including cylindrical focusing electrodeswhich are concentrically positioned between the electrodes of thecylindrical condenser and are symmetric about the center thereof.

These and other objects and features of the present invention willbecome more apparent upon a perusal of the following specificationstaken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic drawing of a preferred embodi merit of the presentinvention and includes a partially cut-away isometric view of thecylindrical condenser portion thereof;

FIG. 2 is a schematic drawing of another embodiment ice showing a topview of the cylindrical condenser assembly shown in FIG. 1 and amodified ion source; and

FIG. 3 is a schematic drawing of another preferred embodiment of thepresent invention illustrating a modification of the cylindricalcondenser assembly shown in FIGS. 1 and 2.

Referring now to FIG. 1, there is shown with the evacuable envelope 8 acylindrical condenser 1 having an inner cylindrical electrode 4 coaxialand coextensive with the hollow outer cylindrical electrode 3. A voltagesource 7 is connected between the outer electrode 3 and the innerelectrode 4, and a magnetic field B is provided parallel to the centralaxis of cylindrical condenser 1 by the magnetic pieces 6.

Ions created or directed within the outer electrode 3 (in a mannerdescribed below) will move towards the inner electrode 4 under theinfluence of the cylindrically symmetrical electric field existingbetween the electrodes 3 and 4. They are, however, deviated from theirpath by the applied magnetic field so that with suitably selected fieldmagnitudes the ions will move past the inner electrode 4 and again reacha point in the neighborhood of the outer electrode, whereby theirvelocity is again reduced towards zero. This process can be repeated asoften as desired.

Since the deflection angle which is described by an ion when traversingsuch an orbit depends upon the specific mass of the ion in addition tothe properties of the fields, the described arrangement can be used forseparating ions according to mass. Furthermore, it is characteristic forthis arrangement that the angle of the deflection is larger for ions ofsmaller mass. If, therefore, field strengths are selected to provide anorbit for a given mass which passes immediately adjacent to the centerelectrode, all ions of larger mass will hit the center electrode and bethereby eliminated. For this reason the present invention isparticularly well suited for use in detecting ions of small mass and,therefore, for use in vacuum applications as a helium leak detector.

In the embodiment shown in FIG. 1 ionization of a sample gas occurs inthe ion source 10 and the resultant ion beam 9 is directed into thecylindrical condenser 1 through an aperture 12 in the outer electrode 3.A focusing electrode 13 is used to direct the ion beam 9 through theaperture 12. The ions of the selected mass are deflected in a given patharound the center electrode 4 and to a point near an aperture 15, whichis situated at a predetermined position in the cylindrical surface ofthe outer electrode 3. The ions of selected mass are attracted throughthe outlet aperture 15 and collected by the collector electrode 16,which is located within the envelope 8. The conventional amplifier andion current sensing device 11 is connected to the collector electrode 16by the electrical lead 14. Ions having other than the selected mass willbe collected by the inner electrode 4. This arrangement can also be usedfor the simultaneous measurement of several differing mass ions byhaving a plurality of outlet apertures and collector electrodes (notshown) positioned at suitable places along the outer electrode 3. Also,the mass spectrometer can be so operated that the ions of selected massmake only one oscillation within the outer electrode 3 before reachingthe collector electrode 16, or they can run through several cyclesbefore reaching a suitably positioned collector electrode and outletaperture.

Ions can also be produced within the cylindrical condenser 1 as shown inFIG. 2 wherein the conventional electron source 18 is positioned withinthe envelope 8 and directs a beam of electrons 17 adjacent the innersurface of the outer electrode 3 and parallel to the applied magneticfield. The electron beam will cause ionization of the sample gasmolecules which have entered the envelope 8 through the sample inlet 19and the outer cylindrical electrode 3 through the open ends thereof. Theresulting ions will respond to the crossed electric and magnetic fieldsin the manner described above.

For certain applications it is desirable to provide the cylindricalcondenser 1 with the cylindrical baffle electrodes 17 and 18, 25 and 26,which are positioned between the inner and outer electrodes and areconcentric therewith. The adjustable potentiometer 27 energizes thebaflie cylinders 25 and 26 with a potential which corresponds to theelectric field potential at their radial position. The apertures 29 arestrategically located in the anticipated flight path of the ions havingthe selected mass. Thus, the ions of selected mass Will be transmittedby the apertures 29 and permitted to exit through the outlet aperture 15for collection by the collector electrode 16. Ions having other than theselected mass will be influenced into different flight paths so as to beintercepted by the solid portions of the baffle electrodes 25 and 26.

The embodiment shown in FIG. 3 is identical to that of FIG. 1 exceptthat the baffle cylinders 25 and 26 are replaced by a pair of separatedfocusing electrode cylinders 31, 32 which are positioned symmetricallyabout the center point of the cylindrical condenser 1. In thisembodiment each pair of focusing cylinders 31, 32 are given slightlymore positive potentials than that of the electric field at their radialposition. This enables the focusing electrodes to help focus ions towardthe longitudinal center of the cylindrical condenser '1 in addition tocollecting secondary electrons formed by the impingement of ions on theinner electrode 4. Additional longitudinal focusing of the ion beam 9can be obtained with the spaced end electrodes 28, which are at aslightly more positive potential than the outer electrode 3.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A mass spectrometer apparatus comprising a solid outer cylindricalelectrode, an inner cylindrical electrode positioned within andconcentric with said solid outer cylindrical electrode, means forapplying a potential between said solid outer cylindrical electrode andsaid innercylindrical electrode so as to produce a cyliudricallysymmetrical electric field therebetween, means for directing a magneticfield in the area between said solid outer cylindrical electrode andsaid inner cylindrical electrode in a direction parallel to the centeraxis of the cyl'indrically electric field, means to provide a supply ofions Within said solid outer cylindrical electrode, the cylinder surfaceof said solid outer cylindrical electrode having an outlet aperture toallow ions of a given mass to pass out of said solid outer cylindricalelectrode, and ion collector means positioned outside said solid outercylindrical electrode for detecting said ions of a given mass.

2. The apparatus according to claim 1 including a cylindrical electrodebafiie positioned between said outer cylindrical electrode and saidinner cylindrical electrode, means for applying a potential to saidcylindrical electrode baflie, and wherein said cylindrical electrodebaffle is provided with apertures positioned to allow passage of ionshaving the given mass.

3. The apparatus according to claim 2 wherein said means for applying apotential between said outer cylindrical electrode and said innercylindrical electrode to provide a more positive potential on said outercylindrical electrode than on said inner cylindrical electrode, andwherein said means for applying a potential to said cylindricalelectrode baffle applies a potential thereto which is intermediate tothe potentials applied to said outer and inner cylindrical electrodes.

4. The apparatus, according to claim 1 including a pair oflongitudinally aligned cylindrical focusing electrodes concentricallypositioned between said outer cylindrical electrode and said innercylinder electrode, means for applying a potential to said cylindricalfocusing electrodes, and wherein said pair of cylindrical focusingelectrodes are separated by a transverse gap therebetween.

5. The apparatus according to claim 4 wherein said means for applying apotential between said outer cylindrical electrode and said innercylindrical electrode applies a more positive potential on said outercylindrical electrode than on said inner cylindrical electrode, andwherein said means for applying a potential to said cylindrical focusingelectrodes applies a potential thereto which is intermediate to thepotentials applied to said outer and inner cylindrical electrodes.

6. The apparatus according to claim 1 wherein said outer cylindricalelectrode contains an inlet aperture and said mass spectrometerapparatus includes an ion source adapted to pass a supply of ionsthrough said inlet aperture into said outer cylindrical electrode tothereby provide the supply of ions within said outer cylindricalelectrode.

7. The apparatus according to claim 6 including a cylindrical electrodebafile positioned between said outer cylindrical electrode and saidvinner cylindrical electrode, means for applying a potential to saidcylindrical electrode bafile, and wherein said cylindrical electrodebaffle is provided with apertures positioned to allow passage of ionshaving the given mass.

8. The apparatus according to claim 7 wherein said means for applying apotential between said outer cylindrical electrode and said innercylindrical electrode applies a more positive potential on said outercylindrical electrode than on said inner cylindrical electrode and saidmeans for applying a potential to said cylindrical electrode baflieapplies a potential thereto which is intermediate to the potentialsapplied to said outer and inner cylindrical electrodes.

9. The apparatus according to claim 1 wherein the apparatus comprisesmeans to provide the supply of ions by inducing gas ionization withinsaid outer cylindrical electrode.

10. The apparatus according to claim 9 wherein said outer cylindricalelectrode contains a gas inlet opening to admit a supply of ionizablegas into said outer cylindrical electrode.

References Cited by the Examiner UNITED STATES PATENTS 2,535,032 12/1950Bennett 250-419 2,735,942 2/1956 Brubaker 250--41.9 3,004,158 10/1961Steimel 2504l.9

RALPH G. NILSON, Primary Examiner.

H. S. MILLER, G. E. MATTHEWS, A. L. BIRCH,

Assistant Examiners.

1. A MASS SPECTROMETER APPARATUS COMPRISING A SOLID OUTER CYLINDRICALELECTRODE, AN INNER CYLINDRICAL ELECTRODE POSITIONED WITHIN ANDCONCENTRIC WITH SAID SOLID OUTER CYLINDRICAL ELECTROD,E MEANS FORAPPLYING A POTENTIAL BETWEEN SAID SOLID OUTER CYLINDRICAL ELECTRODE ANDSAID INNER CYLINDRICAL ELECTRODE SO AS TO PRODUCE A CYLINDRICALLYSYMMETRICAL ELECTRIC FIELD THERBETWEEN, MEANS FOR DIRECTING A MAGNETICFIELD IN THE AREA BETWEEN SAID SOLID OUTER CYLINDRICAL ELECTRODE ANDSAID INNER CYLINDRICAL ELECTRODE IN A DIRECTION PARALLEL TO THE CENTERAXIS OF THE CYLINDRICALLY ELECTRIC FIELD, MEANS TO PROVIDE A SUPPLY OFIONS WITHIN SAID SOLID OUTER CYLINDRICAL ELECTRODE, THE CYLINDER SURFACEOF SAID SOLID OUTER CYLINDRICAL ELECTRODE HAVING AN OUTLET APERTURE TOALLOW IONS OF A GIVEN MASS TO PASS OUT OF SAID SOLID OUTER CYLINDRICALELECTRODE, AND ION COLLECTOR MEANS POSITIONED OUTSIDE SAID SOLID OUTERCYLINDRICAL ELECTRODE FOR DETECTING SAID IONS OF A GIVEN MASS.